First aide kit
The usual suspects
I bought an all-in-one first aide kit put out by the *Tylenol* people, Johnson
and Johnson. It has in it the pain relievers and such that you would expect,
including the children's versions, which work as well on grown humans.

A few additions
In the provided empty containers, I put in vitamins, aspirin, salt tablets
and other things that were not included in the kit, but I felt was necessary.
I also added a few homeopathic preparations for poison ivy and bug bites,
as well as powdered gelatin for the occasional bout of Montezumas revenge.
And dont forget the vinyl gloves!
Vitamins can keep you healthy when you are on the trail. If you use a vitamin
or supplement in your daily life, take them with to keep your body on a even
keel.
Powdered gelatin, my favorite flavor is strawberry, can be very useful in
a survival situation. Eat it raw to keep the effects of diarrhea
down(and your protein up), use it to flavor and thicken foods you have with
you and you can use the flavored type to dye cloth in a pinch. I keep it in
my first aide kit because it is less likely to get wet.
If you know you are going to be doing a lot of walking, consider having some
moleskin in your kit. I personally have not used it, but at least one tenderfoot
I have hiked with goes through a package a trip. It creates a callous
over where your footwear rubs and reduces the likelihood of bad blisters.
In preparation, I would suggest a few books
and resources that can help you find plants that are useful, and ones
to keep away from.
Check the Camping List for more to go into a First Aide kit.
You never know...
I once had an adventure that this first aide kit helped me cope with. My
First Adventure of Self Sufficiency.